This invention relates to a method and apparatus for aligning and positioning a workpiece, such as a lens, so that an axis of the workpiece is precisely aligned with a fixture and a surface of the workpiece is precisely positioned a constant distance from a reference point on the fixture. The invention has particular application in the field of manufacturing contact lenses and intraocular lenses, but it not limited to this application.
In the manufacture of lenses, the degree of accuracy of alignment of a partially finished lens to its fixture, e.g., a mandrel, determines the limit of concentricity possible through subsequent machining operations. A high degree of concentricity is advantageous in the manufacture of lenses since greater concentricity results in less prism. The accuracy of positioning the apex of the lens to a reference point or shoulder of the fixture determines the accuracy of the manufactured lens thickness. A high degree of consistency of lens thickness is advantageous for the manufacture of lenses. Such precise positioning, however, can be time consuming and difficult to obtain if done manually.
An example of the use of this invention is in the manufacture of contact lenses and intraocular lenses. However, the invention is not so limited and the principles of the invention may be applied to the manufacture of other types of lenses or objects other than lenses. For purposes of example only, the process of manufacturing contact lenses will be described.
Contact lenses are typically manufactured by way of a complex multi-step operation whereby the fabricated lens goes through many precision operations. The technique described in U.S. Pat. No. 5,080,482, the disclosure of which is hereby incorporated by reference in its entirety, makes use of a camera and a focusing reticle video image in order to automatically align a lens. The reticle image is focused on the surface of the lens and then analyzed using a focusing algorithm. Although accurate, the process can be time consuming and may be limited to a small range of measurable optical radii.
It is therefore desirable to improve upon the prior techniques, such as described in U.S. Pat. No. 5,080,482, with respect to the possible range of optical radii that can be accurately aligned and positioned as well as to decrease the speed or cycle time of the process. It is desired to allow for quicker measurement of a wide range of radii and optical surfaces beyond sphere radii including, but not limited to, cylinder shapes, toroids, or any geometric figure with a high or low point representing the center of the optic.